Very easily! And could certainly happen accidentally.

I live in spread out suburbs, so my radio spectrum is pretty clear. It might be an issue in a vertically-oriented city.

My primary automation network is ZigBee, which does have a (mild) layer of encryption and mechanisms to prevent replay attacks. There are ZigBee buttons and remotes, but nothing cheap enough that I could put two in every room. (And I had a bunch of these remotes previously, from when I just used them with the matching outlets).

Most neighbours are decent folks, so security may not be necessary. For example, I had an open Wifi for years, so the neighbours could share it if they wanted. I also had passwordless Airplay speakers, and only once soneone tried to play music on them. (Was fun)

At some point I unfortunately had to add a password because someone else used all the bandwidth...